Electron tube device



' N/E. G. BACKMARK ET AL May 25, 1954 ELECTRON TUBE DEVICE 2 Sheets-Sheet 1 Filed June 14, 1950 .BCLCKUZQ/ZLZI y 25, 1954 N. E. G. BACKMARK ET AL ,67 ,610

ELECTRON TUBE DEVICE 2 Sheets-Sheet 2 Filed June 14, 1950 HgJb Patented May 25, 1954 UNITED STATES PATENT OFFICE ELECTRON TUBE DEVICE Sweden Application June 14, 1950, Serial No. 167,956

Claims priority, application Sweden June 21, 1949 4 Claims. 1

This invention relates to electron tube devices of the kind which is described in application Serial No. 122,443, filed October 20, 19 19, now Patent No. 2,591,997, dated April 8, 1952.

This patent relates to electron tube devices with electron tubes, the discharge chamber of which is penerated by a magnetic field and which contains a centrally arranged cathode and a plurality of electrodes surrounding the same, which electrodes by means of different circuit elements or connecting means may be given individually a potential differing from that of the other electrodes. These electrodes may be of two kinds, partly control electrodes, spades, and partly contact electrodes, plates, which last mentioned are arranged between the spades and connected to resistances.

One important field of application for the present invention is in selectors for automatic telephone systems. As the tube has no electron gun nor electro-optical means for generating the electron current which performs the switching,

as do cathode-ray tubes intended for telephone purposes, and as the tube of the present invention is very compact as compared with cathoderay tubes and can be operated at lower voltages,

the improved tube is particularly suited for telephone selection apparatus. The invention can also be utilized as a switch or distributor for multi-channel telephone or signal communication systems using lines or radio links, such switches operating to connect a plurality of transmitters successively and cyclically to a common outgoing circuit. At the receiving end of the transmission medium, a similar switch or distributor would be used, and synchronized with the first distributor, to connect a plurality of receivers for the different channels successively to the transmission circuit.

The invention relates to improvements in this kind of electron tubes for the purpose of increasing the current, which may be derived from the contact electrodes of the tubes. The invention also relates to devices for facilitating the manufacture of such tubes and to means for reducing the magnitude of the parasitic or noise current appearing during the operation of the tubes.

A distinctive feature of the invention is that the ratio between the diameter of the cathode cylinder and the distance between the edges directed towards the cathode of the control electrodes, which are arranged diametrically in the tube in relation to each other, is such, that the whole cathode current, when the electron beam is directed into a certain box formed between adjacent spades, is obtained to the plate situated in this box.

Another distinctive feature of the invention is that a closed cylindrical screen is arranged round the electrode system so as to make degasifying of this electrode system possible by means of high frequency heating at the manufacture of the tube.

A further distinctive feature of this invention is that the electron emitting coating of the cathode cylinder is shaped in sections surrounded by cathode portions without the ability of emitting electrons.

The invention will be more closely described in the following with reference to the annexed drawing, on which Fig. 1 shows a diagrammatic section of an electron tube. Fig. 2 shows a diagram over the current to plates and spades in this tube. Fig. 3a shows diagrammatically the intera-rrangement of the electrodes in the tube shown in Fig. 1. Fig. 3b shows the relation between the cathode diameter and the distance between the edges directed towards the cathode of diametrically opposed spades as a function of the number of spades. Fig; 4 is a perspective view showing an electron tube with certain parts broken away and including means according to the invention.

Fig. 1 in the drawing shows an electron tube, the envelope of which is designated H, a centrally arranged cathode K and a number of spades S1-S1o arranged round the same and alter nating with plates P1 P1o. The spades are all connected to the same voltage V0. Further details not necessary for the comprehension of the following description as resistances etc., are omitted in the figure but may be shaped in the same manner as is described in the main patent.

In such a device with full voltage Voon all the spades the electrons leaving the cathode turn back to the same except for a small leak current dependent on the magnetic field. An electron beam being symmetrical round the cathode is thus obtained, which beam in the figure is designated E1 and is marked with continuous lines.

If the potential of one of the spades, for instance the spade S1 is decreased to the value Vspl Vo) the electron beam will be directed towards this spade and into the corresponding box, where it hits the plate P1 situated within the same. To begin with only a portion of the electron beam will be directed into the box, as is illustrated in the figure by the beam E2 marked with dotted lines.

It is however desirable that the electron beam is completely directed into the intended box, when the spade has obtained cathode potential, i. e. when Vspl= and that, in other words, the beam indicated with E1 ceases and all the electrons emitted from the cathode follow the path indicated with E2 to the plate P1 in the box formed between the spades S1 and S2.

From the diagram in Fig. 2, which shows the cathode and spade current as a function of the spade voltage, is apparent that the cathode current Ikl, which is marked with a continuous curve, reaches an almost constant value, when the spade voltage Vspl is equal to zero, At incomplete deflection of the electron beam to the intended box some electrons will however pass the spade in question, also when this has the potential zero and return to the cathode. Total deflection of the beam to this box will thus not be obtained until the spade voltage gets a negative value, which in Fig. 2 is illustrated with the dotted curve Ik2.

The facts cited above have their explanation in the potential relations between the spade and the cathode and depend on the potential minimum, which is achieved and necessary to have in order to direct the whole beam into the intended box. This potential minimum is dependent on the ratio between the cathode diameter die and the pitch circle diameter for the spade cls defined as the distance between two spades placed diametrically in the tube at the edges of the spades directed towards the cathode, and also on the total number of spades.

If the number of control electrodes for instance is chosen as ten the cathode radius may be chosen arbitrarily for values of said relation dk/ds (Fig. 3a), which exceed a certain limit value. At this limit value the influence from one spade on the field is sufficient to obtain a sufficiently low potential minimum. It has been proved by practical experiments that the cathode current is constant for spade voltages greater or equal to zero at practically all values of the cathode diameter die, if said limit value is exceeded.

In Fig. 3b the relation between the limit value for the ratio dk/ds and the number of spades n within the tube is shown. As appears from this figure the limit value for dk/ds is increasing very rapidly for an increased number of spades and approaches 1, i. e. the necessary cathode diameter die approaches very rapidly the value of the diameter 11$ for the pitch circle of the spades and the distance between the cathode surface and the edges of the spade grows very small. This means that the cathode at values on n exceeding ten very rapidly will be of troublesome dimensions and causes a heavy increase of the noise and the heater current.

The above-mentioned tendency in electron tubes of this kind to demand negative voltage in relation to the cathode for attaining a complete directing of the electron beam to a certain box may thus be counteracted by an increase of the cathode diameter, which however causes other inconveniences, if the number of spades within the tube is too great. The values of the least ratio between the cathode diameter and the diameter of the pitch circle for the edges of the spades, Which are required for obtaining a full cathode current to the plates within the different boxes at the spade potential zero, are at 10, 12 and 14 spades in the tube 0.01, 0.32 and 0.65, respectively, which values have been determined by experiments and are the basis of the relation in Fig. 322. It might however be possible to reduce these values with at least 10% by an especial shaping of the edges of the spades.

At the manufacture of electron tubes according to the main patent there are further inconveniences with the degasifying the different electrodes at the pumping. These electrodes have namely so small dimensions that it is diflicult to heat them by means of high frequency heating.

This inconvenience may according to the invention be removed by surrounding the whole electrode system with a closed cylindrical metal screen S according to Fig. 4 in the drawing. Such a screen can easily be heated by means of high frequency and be brought to such a temperature that a sufficient radiation energy to the surrounded electrode system may be obtained and this may consequently be degasifled at the tube manufacturing without any difliculty.

A screen of this kind involves furthermore other advantages. It may thus be utilized partly for electrostatic shielding. and partly as anode for electron current instead of the plates.

The electron tube shown in Fig. 4 in the drawing contains besides the cylindrical screen also devices for obtaining a homogeneous magnetic field inside the tube, which often has a rather great axial extension. For this purpose suitably a yoke M of magnetic material is arranged, which for instance may consist of a bottom plate B arranged inside the foot of the tube or outside the tube envelope H and having perforations for the connecting leads to the difierent electrodes and of a disc A of magnetic material placed in the upper part of the tube, said disc also carrying the getter G.

We claim:

1. An electron tube device comprising an electron tube having an envelope containing an evennumbered plurality N of planar control electrodes, a cylindrical cathode mounted centrally among said control electrodes, the latter being disposed in pairs lying with their respective inner edges directed towards diametrically opposite portions of said cathode, and an equal number N of receiving electrodes alternating in position with said control electrodes and mounted at a greater distance from the cathode surface than that part of the control electrodes which lies nearest to said surface, means mounted outside said envelope for producing a constant and homogeneous magnetic field penetrating the discharge space of said tube and the field lines of which are parallel to the axis of said cathode, the minimum value of the ratio between the diameter of the cathode and the distance between the edges directed towards the cathode of diametrically opposed control electrodes being related to the number N of control and receiving electrodes by the following:

2. An electron tube device comprising an electron tube having an envelope containing ten planar control electrodes, a cylindrical cathode mounted centrally among said control electrodes, the latter being disposed in pairs lying with their respective inner edges directed towards diametrically opposite portions of said cathode, and

ten receiving electrodes alternating in position with said control electrodes and mounted at a greater distance from the cathode surface than that part of the control electrodes which lies nearest to said surface, means mounted outside said envelope for producing a constant and homogeneous magnetic field penetrating the discharge space of said tube and the field lines of which are parallel to the axis of said cathode, the ratio between the diameter of the cathode and the distance between the edges directed towards the cathode of diametrically opposed control electrodes being greater than 0.01.

3. An electron tube device comprising an electron tube having an envelope containing twelve planar control electrodes, a cylindrical cathode mounted centrally among said control electrodes, the latter being disposed in pairs lying with their respective inner edges directed towards diametrically opposite portions of said cathode, and twelve receiving electrodes alternating in position with said control electrodes and mounted at a greater distance from the cathode surface than that part of the control electrodes which lies nearest to said surface, means mounted outside said envelope for producing a constant and homogeneous magnetic field penetrating the discharge space of said tube and the field lines of which are parallel to the axis of said cathode, the ratio between the diameter of the cathode and the distance between the edges directed towards the cathode of diametrically opposed control electrodes being greater than 0.32.

4. An electron tube device comprising an electron tube having an envelope containing fourteen planar control electrodes, a cylindrical cathode mounted centrally among said control electrodes, the latter being disposed in pairs lying with their respective inner edges directed towards diametrically opposite portions of said cathode, and fourteen receiving electrodes alternating in position with said control electrodes and mounted at a greater distance from the cathode surface than that part of the control electrodes which lies nearest to said surface, means mounted outside said envelope for producing a constant and homogeneous magnetic field penetrating the discharge space of said tube and the field lines of which are parallel to the axis of said cathode, the ratio between the diameter of the cathode and the distance between the edges directed towards the cathode of diametrically opposed control electrodes being greater than 0.65.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,198,323 Wagner Apr. 23, 1940 2,217,774 Skellett Oct. 15, 1940 2,293,368 Stuart, Jr Aug. 18, 1942 2,320,756 Skellett June 1, 1943 2,358,542 Thompson Sept. 19, 1944 FOREIGN PATENTS Number Country Date 351,419 Great Britain June 24, 1931 

